The long-term objective of this research proposal is to define the poorly characterized mechanism of homologous recombination in Herpes Simplex Virus Type 1 (HSV-1). A better understanding of this aspect of the basic biology of this important pathogen may contribute to more effective therapeutic strategies. Three specific aims are being undertaken in this proposal that exploit the ability of the HSV-1 DNA replication proteins to mediate homologous recombination. First, a recombinant HSV-1 will be generated that lacks the alpha sequence at the L-S junction and tested for the ability to undergo genome isomerization. Second, the mechanism of homologous recombination induced by double-strand breaks generated by EcoRI and cellular topoisomerase II will be investigated. Finally, the ability of the HSV-1 replication proteins expressed by recombinant baculoviruses in Sf9 cells to mediate homologous recombination will be examined and compared with reactions mediated by HSV- 1; this system will also be used to determine if HSV- 1 participates in replication- dependent-~recombination or recombination-dependent-replication. These results will help to elucidate the mechanism of homologous recombination in HSV-1 and nay provide important insight into this phenomenon in human cells.